An automatic reset circuit is used to restart a circuit such as a microprocessor based circuit after a power interruption. Such reset circuits have not operated reliably in many cases, such as when there are multiple short power interruptions within a short period of time, or when the voltage from a power supply drops only a small amount to a marginal value of the operation voltage required by the microprocessor based circuit.
In such cases data corruption and unreliable resetting, including lock-up, can occur.
In attempts to avoid the aforenoted problems, circuits have been designed which block enable inputs of random access memories used in microprocessor based circuits, after power supply voltage decays to a level slightly above (e.g. 4.7 volts) the marginal value (e.g. 4.5 volts) of its operation voltage (5.0 volts). These circuits drain some current from a battery assigned for memory backup, which shortens battery life. Some circuits produce a reset pulse after the operation voltage restores. None of these circuits have been able to reliably provide a reset pulse beginning immediately when the operation voltage drops and ending when the operation voltage has reliably become restored.